The invention is directed to an arrangement for coupling at least two waveguides to one another with each waveguide having at least one core layer for guiding an optical wave having a specific wavelength .lambda..
Arrangements for coupling optical waveguides to one another have numerous applications in the realization of components and for offering connections between optical components in integrated optics.
Most arrangements for coupling optical waveguides to one another use butt coupling (see, N. J. Frigo et al "A Wavelength-Division Multiplexed Passive Optical Network with Cost-Shared Components", IEEE Photonics Technology Letters, Vol. 6, No. 11, November 1994, pp. 1365-1367). The end of a waveguide having a specific lateral or transverse structure thereby strikes against another waveguide having a different lateral or transverse structure. The most obvious manufacturing method uses etching for removing the core of a waveguide and epitaxial growth of the second waveguide with MOVPE or MOMBE. The advantage of this method is the independent selection of the material compositions and dimensions of the two waveguides. However, the difficulty of epitaxial crystal growth at the abutting location exists that this requires the utilization of the edge zones of the epitaxially grown material.
When only a slight difference in the material composition of the two waveguides is required such as, for example, for the integration of a laser and modulator, then mask-dependent, selective epitaxy is available as a relatively simple manufacturing method. Compromises must thereby be accepted in the laser function or modulator function (see M. Aoki et al "Monolithic Integration of DFB Lasers and Electroabsorption Modulators Using In-Plane Quantum Energy Control of MQW Structures", International Journal of High Speed Electronics and Systems, Vol. 5, No. 1 (1994), pp. 67-90), such as:
1. Mask-dependent, selective epitaxy allows only slight variation of the wavelength of the photo luminescence (PL) between 1.57 and 1.46 .mu.m and is coupled with a variation of the layer thickness. PA1 2. Due to the waveguide section in the region of the band edge transition having a length of approximately 50 through 70 .mu.m corresponding to the gas diffusion length in the MOVPE, additional absorption losses arise (0.5 B at 50 .mu.m length and 1.55 .mu.m wavelength). PA1 3. When the modulating electrical field extends in this region with variable PL wavelength and layer thickness, the light that passes through can be spectrally broadened (chirp). PA1 High-power laser diode with window structure for avoiding "hot spots" at the light exit face. PA1 DBR lasers without butt coupling between amplifier and mirror area for suppressing unwanted reflexes at the transition. PA1 Laser diode or amplifier with taper for cost-beneficial coupling to an optical fiber waveguide or planar light wave circuit (PLC) of, for example, a bidirectional module. PA1 DFB laser diode with external modulator for, for example, wavelength-division multiplex or long-distance system. PA1 Modulator with optical amplifier for, for example, cost-beneficial access to fiber-to-the loop (FTTL) system, for example with the architecture of the RITE network (see the above-mentioned article by N. J. Frigo et al and an article by U. Koren et al, "Polarisation Insensitive Semiconductor Optical Amplifier with Integrated Electroabsorption Modulators", Electronics Letters, Vol. 32 (1996), pp. 111-112) of Lucent Technologies.
It is simplest to employ the same layer packet for the various optical components (see D. Wake, "A 1550-nm Millimeter-Wave Photodetector with a Bandwidth-Efficiency Produce of 2.4 THz", Journal of Lightwave Technology, Vol. 10, No. 7, July 1992, pp. 908-912; A. Ramdane et al, "Very Simple Approach for High Performance DFT Laser-Electroabsorption Modulator Monolithic Integration", Electronics Letters, Vol. 30, No. 23, Nov. 10, 1994, pp. 1980-1981; and A. Ramdane et al "Monolithic Integration of InGaAsP--InP Strained-Layer Distributed Feedback Laser and External Modulator by Selective Quantum-Well Interdiffusion", IEEE Photonics Technology Letters, Vol. 7, No. 9, September 1995, pp. 1016-1018). In this method, the losses in the component properties are especially high since an optimization can only ensue to a limited extent, for example by employing mechanically stressed quantum wells and barriers or by partial re-ordering (disordering) of quantum wells.
Vertically structured waveguide ends (see G. Muller et al, "Tapered InP/InGaAsP Waveguide Structure for Efficient Fibre-Chip Coupling", Electronics Letters, Vol. 27, No. 20, Sep. 26, 1991, pp. 1836-1837; and G. Wegner et al, "Highly Efficient Multi-Fiber-Chip Coupling with Large Alignment Tolerances by Integrated InGaAsP/InP Spot-Size Transformers", ECOC '92. Berlin, pp. 927-930) or laterally structured waveguide ends (see R. N. Thurston et al, "Two-Dimensional Control of Mode Size in Optical Channel Waveguides by Lateral Channel Tapering", Optics Letters, Vol. 16, No. 5, Mar. 1, 1991, pp. 306-308; J. G. Bauer et al, "High Responsivity Integrated Tapered Waveguide PIN Photodiode", Proc. 19.sup.th Europ. Conf. Opt. Commun. (ECOC '93), Vol. 2, Montreux, Sep. 12-16, 1993, paper Tu 28 (p. 277-280); and R. E. Smith et al, "Reduced Coupling Loss Using a Tapered-Rib Adiabatic-Following Fiber Coupler", IEEE Photonics Technology Letters, Vol. 8, No. 8, August 1996, pp. 1052-1054) are employed for waveguide couplers in other works. The core or a cladding layer of the waveguide is thereby tapered such that the optical field is transferred into other regions of this waveguide.
Arrangements for coupling optical waveguides to one another have numerous applications in the realization of components and for offering connections between optical components in integrated optics.